Project Summary/Abstract Obesity is a major independent risk factor for the development of cardiovascular disease. Both human and animal studies demonstrate that a chronic high fat diet (HFD) leads to reduced nitric oxide (NO) bioavailability and endothelial dysfunction. The cycles of feeding and fasting are known to influence the risk for obesity, cardiovascular, and cardiometabolic disease. Ad libitum chronic HFD disrupts the normal circadian rhythm in metabolism and molecular clock gene rhythm in mice. However, specific circadian-dependent mechanisms affecting the endothelium during chronic HFD are poorly understood. Endothelial function under normal activity is known to follow a circadian rhythm peaking during the active period. The mechanisms underlying endothelial dysfunction mediated from loss of circadian rhythms in metabolism remain unknown, and these studies will be beneficial to understand how disruption of metabolic rhythms may lead to circadian dysfunction. A large number of drugs target circadian genes and may be influenced by timing. Chronotherapy is the timing of medications to be synchronized with circadian rhythms to optimize treatment and may be beneficial for treatment of cardiometabolic disease. A better understanding of the circadian-dependent mechanisms leading to endothelial dysfunction and loss of NO bioavailability is necessary for the development of improved therapies or to optimize timing of current therapies.